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of paraxonemal bodies in Tetrahymena paravorax and Glaucoma ferox , two ciliates that are predatory, and sometimes cannibalistic . Perhaps, the develop- ment of these paraxonemal bodies increases the capture efficiency of these predators. The oral cavity of hymenostomes , and particularly its organization and development in Tetrahymena , has been the subject of both extensive and intensive investigations (Forer, Nilsson, & Zeuthen, 1970; Frankel, 1991; Frankel, Jenkins, Bakowska, & Nelsen, 1984a; Frankel, Nelsen, Bakowska, & Jenkins, 1984b; Nilsson, 1976; Williams & Bakowska, 1982). The oral polykinetids of hymenostomes are characterized as membranelles . The membranelle is typically oriented transversely in the oral cavity, has postciliary microtubular ribbons associated with the right-most row of kinetosomes, has no alveoli between the rows, and has parasomal sacs distributed irregularly between the kinetosomes. Membranelles have been characterized as being linked within by distal and proximal filamentous systems and between by a proximal filamentous system (Grain, 1984; Grain & de Puytorac, 1976). This structure has been observed in Tetrahymena (Nilsson, 1976), Glaucoma (Peck, 1978), and Colpidium (Lynn & Didier, 1978). Nevertheless, Peck (1977a, 1978) makes a reasonable argument against this view, suggesting that there is consider- able variation. A case in point is the hymenostome Turaniella , a predator on other ciliates. Its oral cavity is much-expanded and its oral polykinetids and underlying filamentous systems are extremely well-developed, bearing some resemblance to the peniculines with which it was formerly associated (Iftode & Grain, 1975; Iftode, Versavel, & Didier, 1970). However, the ultrastructure of its somatic cortex and its stomatogenesis demonstrated clear affinities to the hymenostomes with which it is now 15.4 Oral Structures 311 312 15. Subphylum 2. INTRAMACRONUCLEATA: Class 9. OLIGOHYMENOPHOREA classified (Didier, Iftode, & Versavel, 1970; Iftode et al., 1984). It is very likely, therefore, that the complicated fibrillar systems of the oral structures of Turaniella have converged on the peniculine model, correlated with the predatory feeding pref- erence of this macrostomatous hymenostome . Functioning of the hymenostome oral apparatus has been elucidated by studies on other macros- tomatous hymenostomes , Tetrahymena vorax and Tetrahymena paravorax . The macrostome forms of these species have an expanded oral region with a large cytopharyngeal pouch in which to capture ciliate prey. The oral apparatus is modi- fied, through morphogenesis , from that of the microstome form by increasing the number and arrangement of kinetosomes in the paroral and oral polykinetids (Smith, 1982). Food vacuoles appear to be formed by a contractile mechanism that involves the microtubules of the ribbed wall, which extends from near the kinetosomes of the paroral, and contractile proteins around the cyto- stome (McLaughlin & Buhse, 2004; Méténier, 1984b; Smith-Somerville & Buhse, 1984). The disruption of food vacuole formation by actin antagonists, such as cytochalasin and latrunculin B , implicates this filamentous protein in the process (Grønlien et al., 2002; Zackroff & Hufnagel, 2002). Exploitation of genetic constructs in Tetrahymena has now corroborated the important role of actin in food vacuole formation (Williams et al., 2006) and, in association with myosin , in the movement of food vacuoles through the cytoplasm (Hosein, Williams, & Gavin, 2005). The ribbed wall micro- tubules of the microstomatous Tetrahymena spe- cies have also been implicated in feeding (Sattler & Staehelin, 1979). Once the phagosome is formed, digestion occurs in a process very similar to that of Paramecium , except that acidosomes are not involved (Nilsson, 1976, 1979, 1987). As has been reported from Paramecium , membrane retrieval and recycling likely occurs from both the early phagosome during its condensation stage and after its fusion with the cytoproct (Mislan & Smith- Somerville, 1986). The peritrichs , as their name suggests, are char- acterized by having ciliary structures around the perimeter of the peristome (Fig. 15.3). Two oral structures are involved \u2013 the paroral , tradition- ally called the haplokinety , and oral polykinetid 1, traditionally called a polykinety . These two structures circle the peristome in a counter-clock- wise direction, if viewed from the top, up to five times in some Campanella species. They then plunge into the oral cavity, traditionally called the infundibulum . The peritrich oral polykinetid 1 is composed of three rows, parallels the paroral in its counter-clockwise course into the infundibulum , and terminates near oral polykinetids 2 and 3, which lie deeper in the infundibulum . Similar to other oligohymenophorean oral polykinetids , there are postciliary ribbons associated with the kineto- somes of the rightmost row, sometimes only visible during stomatogenesis (Bradbury, 1965; Eperon & Grain, 1983; Maslin-Leny & Bohatier, 1984). Alveoli are absent between the polykinetidal cilia, parasomal sacs may be distributed between the kinetosomes, and a complex set of fibres and fila- ments links the kinetosomes to each other and to a filamentous reticulum bordering the leftmost row. These features have been observed in Opisthonecta (Bradbury), Trichodina (Hausmann & Hausmann, 1981a; Maslin-Leny & Bohatier), Thuricola (Eperon & Grain), Tripartiella (Maslin-Leny & Bohatier), and Astylozoon (Guinea, Gil, Serrano, & Sola, 1990). There has been much speculation about these diver- gent filamentous structures compared to those of the oral polykinetids of other oligohymenophoreans . It is most likely that they are correlated with the highly contractile ability of peritrichs , which can bring all their oral ciliature \u201cinside\u201d the peristome as they with- draw from irritating stimuli. The peritrichs create filtering-feeding currents by metachronal beating of the cilia of the paroral and oral polykinetid 1. This creates a \u201cperistaltic\u201d flow between the cilia that traps particles and forces them into the infundibulum where the par- ticles are essentially trapped on the deeper paroral cilia before being directed to the food vacuole (Fenchel, 1980a; Sleigh & Barlow, 1976). Oral ribs direct particles, on the outside, to the cyto- stome, while, on the inside, the ribbed wall micro- tubules direct diskoidal vesicles to the cytostome where they fuse to form the nascent phagosome (Allen, 1984; McKanna, 1973b). As in other cili- ates, excess membrane, as cup-shaped vesicles , is removed from the early phagosome and recycled to the food vacuole forming region (Goff & Stein, 1981; McKanna). The paroral , stichodyad or haplokinety is a typical feature of the oral apparatus of the four preceding classes. Stichodyad refers to the diki- netid nature of this paroral, with the pairs of kinetosomes so oriented after stomatogenesis that they are almost perpendicular to the long axis of the paroral so that the postciliary ribbons of the more oral or inner kinetosome are \u201con the left\u201d (Grain, 1969, 1984). Haplokinety refers to there being only one, the outer, of the two kinetosomes ciliated (Grain, 1984; de Puytorac & Grain, 1976). While there are variations in the nature of the links both that connect the kinetosomes of each dikinetid and that link dikinetids together in the paroral, this basic structure is typical of the oligohymenopho- rean paroral . It has been reported, for example, in the following: the peniculines Paramecium , Frontonia , and Urocentrum (Didier, 1971); the scuticociliates Cinetochilum , Myxophthirus , and Paranophrys (Didier & Wilbert, 1976; de Puytorac et al., 1974a; Da Silva Neto,